Previously the CLI would emit a warning about missing configuration
file, but a configuration file does not appear to be a requirement, at
least based on the documentation and the fact that everything can be
specified directly on the command line.

This commit simply removes the warning.

Users will no longer get a warning when doing things like `floaty
--version`, `floaty help`, and any other subcommand.

So users can be aware of the configuration file since it will no
longer be emitted as a warning during CLI invocation.

To support usage without a configuration file.

Prior to this commit, when using --service=abs and --json the job_id
value is not included in the JSON blob, which makes it difficult for
calling code to grab both the job_id and the hosts without text
processing the log messages printed to standard error.